Earlier quoted context omitted.
I wouldn't read too much into that. nginx is good at serving dynamic content too. Simple setup with uwsgi for Python and php-fpm for PHP.
I think both fpm and wsgi would fall under what OP called "proxying to application servers", despite using a different protocol. Yes it's technically "serving", but so is proxying and literally anything else a "server" does. Maybe "hosting" is a better term: both can serve any content, including dynamic, but apache can often host it as well (without an external server), which nginx can't do nearly as well.
> Considering nginx is really just good at serving static content...
That's not correct at all. Regardless of how the request handled, serving dynamic content on nginx is trivial.